Exams and Tests

Most infected people will have no physical findings, but on physical examination, some will have enlarged cervical lymph nodes (most common physical finding), or an enlarged spleen or liver. People with moderate to severe infections may exhibit jaundice (especially infants) or increased bruising due to liver involvement, eye problems (decreased vision or blindness), meningoencephalitis (inflammation of the brain and linings of the brain), seizures, pneumonitis, and mental-status changes. Unfortunately, many other diseases can cause similar mild and severe symptoms (for example, Chagas' disease, giardiasis, malaria, cat scratch disease, brain abscesses, sepsis, cytomegalovirus, and many others). Fortunately, there are a number of tests that can help differentiate toxoplasmosis from other diseases and provide evidence for a presumptive or definitive diagnosis.

The definitive diagnosis of toxoplasmosis is made by identifying Toxoplasma gondii organisms in blood, body fluids (for example, spinal or amniotic fluid), or tissue (biopsy samples). In addition, body fluids can be injected into mice; the animals will develop the disease if the parasites are in the injected body fluid. Also, body fluids can be inoculated into cell cultures where the parasites can proliferate. These tests are usually done in specialized laboratories by experienced personnel.

Other tests can yield a presumptive diagnosis and are based on the person's immune response to the parasite. Body fluids can be tested by PCR and there is an enzyme-linked immunosorbent assay (ELISA) technique that can indicate acute infection. Another test, the Sabin-Feldman test, measures the patient's IgG antibody directed against the parasites and is a standard reference test for toxoplasmosis. IgG antibodies indicate that infection with toxoplasma has occurred in the past but does not tell whether the current infection is due to T. gondii. Other tests detect IgM antibodies directed against the parasite and may detect these antibodies as early as the first week of infection. Most often, these tests are done by specialized laboratories. The timing of these tests is important as is the interpretation of the results. Some people may have positive results because the person has been previously exposed to the parasite and the person may actually have another disease causing the symptoms. Consultation with an infectious diseases expert may help determine the diagnosis when only presumptive evidence of Toxoplasma infection is available.

Pregnant individuals and those planning to become pregnant can get tested with immunological tests similar to those listed above for presumptive diagnosis to determine if there is a risk for the mother to transmit Toxoplasma infection to the fetus. If the woman has no antibodies in her bloodstream, she is susceptible to getting the disease and could be monitored more closely and educated.